Conventionally, a user interface device for a vehicle mounted device, such as a car navigation system, is proposed. In such a proposed device, a hand of an operator is taken as an image by a camera, then, the device extracts a finger image from the image data, and displays the extracted finger image area on an input display screen of GUI, Graphical User Interface system, for the vehicle mounted device. For example, the extracted finger image area is displayed on a screen of the car navigation system. For example, the following patent document 1 discloses a device which uses a camera attached on a ceiling of the vehicle. In this device, the camera takes an image of a hand which is placed to operate a switch panel disposed next to a seat. Then, the device displays the image of the hand and the switch panel on a liquid crystal panel disposed on a forward side of the operator. The following patent document 3 discloses a device in which a finger-shaped image is displayed in a superimpose manner. The finger-shaped image is different from the hand image taken by the camera. The finger-shaped image is narrower than the finger on the hand image. The finger-shaped image is placed on a corresponding finger position located from the hand image.
On the other hand, several methods and system for determining and locating a fingertip position on an image of a hand is proposed. For example, the patent document 2 discloses a method in which a finger is assumed to be stretched, and a fingertip position is located by an approximation using a circumscribed ellipse. The patent document 3 discloses a method in which an image of a finger is taken in a perspective manner from a distal end side to take an outer profile of the finger pad. In this method, the fingertip position is determined based on the pole of a high-order function which is obtained by approximating the outer profile of the finger pad. The patent document 3 discloses a method in which a circumscribed rectangle on the image taken is divided into two or more sub-rectangular areas. Then, it is determined that whether a shape on the image is considered as a shape which is not necessary for locating the coordinates of the fingertip based on a ratio of areas of the sub-rectangular areas or not.